This application claims the priority of German patent application number 196 41 763.5, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a mass damper with variable resonant frequency for a dynamically-excited part, and more particularly to a mass damper with a housing connected in a vibration-free manner with the part and with a spring-mass system that can vibrate in the direction of the excitation of the part, said system consisting of a leaf-spring arrangement tensioned at one side integrally with the housing and on the other side provided with an inertial mass at the free end of the spring.
Mass dampers of this type can be used wherever periodic excitation of a part is to be compensated, for example in helicopters to counteract vibration phenomena on helicopter parts, especially cockpit parts, that are dynamically excited by the rotor system of the helicopter at the rotational frequency of the rotor.
Mass dampers with variable resonant frequency are required for modern helicopters that are operated with a variable rotor rpm. For this purpose it is known to displace, on the outer oscillating inertial mass of a leaf-spring mass system, using a positioning drive controlled by an electric motor, differential masses in the lengthwise direction of the leaf-spring arrangement in order thereby to adapt the natural frequency of the mass damper continuously to the exciting frequency of the rotor system. A frequency-adjusting mechanism of this kind in the oscillating part of the spring-mass system however entails a relatively high construction cost and is subject to high acceleration at high load alternation values, so that service life problems can develop.
An object of the invention is to provide a mass damper of the type described generally above that uses a structurally simple and problem-free resonant frequency adjustment in the non-vibrating area of the spring-mass system.
This and other objects have been achieved according to the present invention by providing a mass damper for a vibrating part, comprising: a housing fixedly coupled to the vibrating part which vibrates in an excitation direction; a leaf spring fixedly coupled to said housing at a connection area and having ends extending from said connection area perpendicular to said excitation direction; and a support system operatively coupled to the leaf spring and the housing, said support system being adjustable to vary a biasing force of the leaf spring on the housing in said excitation direction.
This and other objects have also been achieved according to the present invention by providing a mass damper with variable resonant frequency for a dynamically excited part, comprising: a housing connected in a vibration-free manner with the part; a spring-mass system connected to said housing, said system being vibratable in an excitation direction of the part, said system including a leaf-spring arrangement tensioned integrally with the housing and an inertial mass fixedly coupled to a free end of the leaf-spring arrangement; and a support operatively coupled between the leaf-spring arrangement and the housing, said support being adjustable to vary a tension of the leaf-spring arrangement relative to the housing.
This and other objects have also been achieved according to the present invention by providing a method of damping vibrations of a dynamically excited part, comprising: connecting a housing with the part in a vibration-free manner; connecting a spring-mass system to said housing such that said system is vibratable in an excitation direction of the part, said system including a leaf-spring arrangement tensioned integrally with the housing and an inertial mass fixedly coupled to a free end of the leaf-spring arrangement; and operatively coupling a support between the leaf-spring arrangement and the housing such that said support is adjustable to vary a tension of the leaf-spring arrangement relative to the housing.
This and other objects have also been achieved according to the present invention by a method of damping vibrations of a vibrating part, comprising: fixedly coupling a housing to the vibrating part which vibrates in an excitation direction; fixedly coupling a leaf spring to said housing at a connection area such that ends of the leaf spring extend from said connection area perpendicular to said excitation direction; and operatively coupling a support system to the leaf spring and the housing such that said support system is adjustable to vary a biasing force of the leaf spring on the housing in said excitation direction.
According to the invention, as a result of the support acting between the housing and the leaf-spring arrangement with variably adjustable tensioning geometry or spring stiffness, a situation is achieved in which the bending elasticity of the spring arrangement and hence the resonant frequency of the mass damper can be changed solely by an adjusting mechanism located on the housing side and therefore in the non-oscillating area of the spring-mass system, thus eliminating structurally complex and dynamically high-loaded mass displacement drives integrated into the vibrating part of the system.
In another preferred embodiment of the invention, the tensioning geometry of the support is modified such that the leaf-spring arrangement contains at least two individual springs located one above the other and permanently connected together on the side facing the inertial mass, the mutual spacing of said springs at the tensioning point being variably adjustable, via the support, transversely with respect to the extension of the surface of the leaf-spring arrangement. With such support of the double leaf spring with variable spacing, by means of the bending resistance moment, the bending stiffness and hence the resonant frequency of the spring-mass system is influenced in an especially simple fashion structurally by control interventions on the housing side.
According to another preferred embodiment of the invention, which can also be used for mass dampers with a single leaf spring, the effective leaf spring length and hence the resonant frequency is influenced by a variable-length tensioning geometry in such fashion that the support of the leaf spring on the housing side contains two pressure elements, each of which abuts one side of the leaf spring with an adjustable tensioning length, said pressure elements, in a structurally advantageous design, each comprising a tensioning spring that is bent convexly in the direction of the leaf-spring arrangement and is pressed against the leaf-spring arrangement in a contact zone of adjustable length.
In another preferred embodiment of the invention, the flexible support, for reasons of structural simplification, preferably contains mechanical compression springs with a nonlinear spring characteristic and variably adjustable spring pretensioning, with nonmetallic spring elements, for example gas springs with variably adjustable spring hardness, possibly being used as support springs instead of coil springs.
With an eye toward simple design for the adjusting mechanism for changing the tensioning geometry or spring stiffness, the mechanism according to one preferred embodiment comprises an adjusting spindle, rotatably mounted on the housing, and two supporting members, said members, following a change in the pivot point of the spindle, being adjustable in opposite directions with respect to one another and transversely with respect to the extension of the leaf-spring arrangement.
According to further preferred embodiment, the mass damper is preferably provided with a control unit by which the resonant frequency of the mass damper is controlled adaptively to adjust to the changes in the exciting frequency.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.